The present invention relates to pressure measurement devices, and more particularly to an implantable pressure measurement device that provides physiological pressure information via an external imaging system.
Pressure measurement devices of various types are used to measure a physiological pressure in different areas within the body of a patient. One application of such devices is in the treatment of hydrocephalus, a condition where cerebrospinal fluid (CSF) collects in is the ventricles of the brain of a patient. CSF is produced by the choroid plexis in the ventricle system and is normally absorbed by the venous system. However, if an unbalance between CSF production and the absorption of the CSF occurs, the volume of CSF increases thereby elevating the intracranial pressure. This excess CSF can result in abnormally high epidural and intradural pressures. Left untreated, hydrocephalus can result in serious medical conditions, including subdural hematoma, compression of the brain tissue and impaired blood flow that consequently can impair cognitive and motor function.
To determine the intracranial pressure, a pressure measurement device can be inserted into the patient to measure the pressure. One such device is a catheter having a sensor for in vivo measurement of intracranial pressure in which one end of the catheter is disposed in the ventricular region of the brain and the other end exits the cranial region for coupling to a monitor. The measurement of intracranial pressure with such a device is an invasive procedure having certain concomitant risks, such as infection and human error. Thus, monitoring intracranial pressure with this type of device is best suited for short term use only.
Once it is determined that intracranial pressure is above acceptable levels, the pressure should be relieved. Various drainage catheters or shunt systems have been developed to remove the excess CSF and to discharge the fluid to another part of the body, such as the peritoneal region. By draining the excess fluid, the elevated intracranial pressure is reduced.
Generally, CSF shunt systems designed for long term use are implantable within the patient. Such CSF shunt systems include a valve mechanism for controlling or regulating the flow rate of fluid through the system. An illustrative shunt system includes a valve mechanism in fluid communication with a brain ventricular catheter. The ventricular catheter is inserted into a ventricle of the brain and a peritoneal catheter is inserted into the peritoneal region for discharge of the fluid. While such implanted catheters can drain excess CSF if working properly, intracranial pressure information is not readily available without an invasive surgical procedure.
Shunt systems typically permit fluid flow only when the fluid pressure reaches a threshold pressure for the shunt valve. The threshold pressure that allows fluid flow through a shunt system must sometimes be adjusted. For example, a surgeon may initially select a relatively low threshold pressure to trigger fluid flow. Over time, the initial threshold pressure may not be ideal. For example, it could lead to excess fluid flow, creating an undesirable overdrainage condition caused by too much fluid being drained from the ventricle. A CSF overdrainage condition can result in a dangerously low intracranial pressure. Such a situation may give rise to a need to increase the threshold pressure to afford a fluid flow rate that is balanced to avoid both excessive intracranial pressure and overdrainage conditions.
Some shunt systems can become clogged or may malfunction mechanically. When a patient exhibits symptoms that could be related to shunt malfunction it is often desirable to evaluate whether the shunt system is functioning properly and/or to evaluate intracranial pressure directly. If the threshold pressure is set too high, or if the valve is occluded, excessive CSF will not be discharged via the shunt system to relieve intracranial pressure. If the threshold pressure of the valve mechanism is set too low, or if the valve is stuck open, a CSF overdrainage condition can occur. Shunt system operation can be monitored by observing the pressure on fluid in the shunt system. However, as discussed above, monitoring the pressure of an implanted shunt system can require an undesirable invasive surgical procedure.
An implantable pressure measurement device is needed that provides physiological pressure information, without invasive surgical procedures. It would also be desirable to monitor the operation of certain implanted devices, such as fluid shunt systems.